Shed Roofs
Shed roof systems are a simple form of roof structure well suited to modest sized buildings where conditions preclude the even simpler flat roof. It is well suited to seasonal or temporary structures. It generally will employ alloy panel cladding but also offers one of the simplest approaches to using tensile roofs as a variant of the detached or ‘skybreak’ roofing concept, which we will discuss in more detail in another section. Shed roofs have two basic forms; single plane and compound. The single plane shed roof covers an entire structure in one plane surface like a flat roof. It is usually relatively shallow in slope with wide roof overhangs. The compound or split shed roof employs two planes that meet over a common Primary post line, one with a steeper slope than the other so as to overlap where they meet. This can provide a simple approach to expansion of an existing single plane structure. With Utilihab, shed roofs are supported by mounting roof joists on-top the top of the Primary frame. To create the slope of the roof, one end of the Primary frame employs a riser. For a shallow sloped roof this can simply be a single span of Primary frame profile attached to the top of the parallel main Primary frame. It will usually have a length long enough to accommodate a roof overhang. Where possible, a single double, triple, or quad height profile may be employed as the Primary horizontal member on this end, as in the case of the Light Primary framing and its option to use a 100x200mm or taller profile for this riser. This is matched in length to standard height Primary beam on the opposite end and both are fashioned to ride over the top of shortened vertical posts with the alternate side Primary beams attaching to them rather than the posts, connecting to tension plugs in the top of the posts. For steeper slopes, a riser truss is created as per conventional profile truss methods. This can employ either truss plates which fit in the standard profile slots or profile cross braces sized to suit the riser height. Taller risers may require additional reinforcement using angle consoles or profile braces along their inside corners. In some cases risers may be employed on both ends of the structure in order that, with the roof overhang, the low end still meets a minimum 2400mm height. Where compound shed roofs are employed, the high end riser is modified to include an upper and lower roof tie beam, one at the top of the riser truss and the other mounted on its side and using through-bolt and/or angle attachment to vertical members along the truss. (A standard truss will usually employ only angled braces or solid truss plates but for the compound shed roof several vertical posts are added in-line to mount this additional tie beam) Rafters made of 50x100mm 1x2 Secondary framing are then attached using T-nuts and inside-edge angles matched to the roof slope or standard profile hinges adapted to serve as variable angles. Additional reinforcement can be added with side angle plates matched to the exact roof slope. Depending on the type of roof cladding used, purlins -usually a 50mm square profile- in the form of short flush Secondary framing spacers or continuous surface-mount beams are then attached to these main rafters. For larger spans the shed roof may need to employ a ‘half truss’ arrangement where the rafter beam is formed into a complete truss with the addition of a bottom tie beam, end post, and diagonal braces. These are installed with perpendicular spacers and diagonal braces along the high end and additional purlins along the slope to tie the truss units together. For compound shed roofs, the high end posts may be shared by the two halves of the shed, functioning akin to a ‘king post’, the lower half-truss connecting to the post’s profile side, the upper half truss rafters overhanging the top of the post. Shed roofs will generally employ surface mounted alloy panel cladding attached as per the methods described for flat roofs. However, special alloy flashing or surface mount wall panels must be added to accommodate the sloped spaces along the roof sides and the end risers. Shed roofs also may employ a detached roof approach. Usually both ends of the roof will have risers and the top surface of the Primary frame will employ flush panels of fiber-cement sealed in aluminum tape. Alternatively, a complete walkable floor deck can be added where there is sufficient space under the roofing, usually based on using fiber-cement under-floor panels and the standard perimeter deck system or some other resilient floor panel. The basic shed roof system is also well suited to fabric or membrane roofing which can attach to a smaller number of wider-spaced rafters using the same snap-lock strip approach of flat membrane roofing. The detached roof finishing approach is used and The roof membrane or fabric is pre-fabricated with U-channel snap-lock strips which plug right into the top profile slot. In some cases simple attachments like GripClips, with their foundation attached by T-nuts, may be usable with plain membrane or fabric sheets. This is especially well suited to modest sized temporary structures. Membrane or fabric roofs may also often employ a deliberate sag between the rafters, rather than being fully tensioned, to create a tent-like look.